Automatic Transfer Switch (ATS) systems are widely used to control the delivery of power from two different power sources to a load in a variety of situations, both commercial and residential. For example, a private residence normally receives its electrical power from a utility company. For various reasons, however (e.g., location in a region prone to severe weather), the homeowner can desire a backup source of electrical power, so that comfort or at least habitability of the residence can be maintained during periods in which utility power is unavailable.
Typically, a gasoline, diesel, propane or natural gas internal combustion engine-powered electrical generator, capable of generating three-phase power, is installed in or near the residence, and arranged to be connected to one or more of the electrical circuits in the residence in order to provide the desired backup power. However, one cannot simply leave the backup generator permanently connected, in parallel with the utility power, to the residential electrical circuits. Nor can one simply power up a backup generator and connect it to the residential electrical circuits, without first disconnecting the residential circuits from the power lines coming in from the utility.
To effect the proper switching of the residential electrical circuits or other load from the utility to the backup generator (and eventually back again to the utility), transfer switch systems can be employed. While manual transfer switch systems are available, ATS systems have become popular insofar as an ATS system is able to automatically switch from one power source (e.g., the utility) to another power source (e.g., the backup generator) whenever the system detects that the one power source is not properly providing power, without the intervention of a human operator.
In order for an ATS system to switch between providing power to a load from one AC power source and providing power to the load from a second AC power source, the two AC power sources must be in phase. Conventional ATS systems rely upon the fact that a generator almost never has exactly the same frequency of operation as the utility (which is exactly at 60 Hz). Consequently, it is almost always the case that, if the ATS system waits for a short period of time, the power signals of the two power sources will come into phase with one another for an instant, at which the ATS system can switch between the two power sources.
However, modern generators increasingly operate at frequencies that are almost identical to the exact (60 Hz) frequency of the utilities. Consequently, it may no longer be practical for an ATS system to wait until the generator power signal happens to come into phase with the utility power signal, since this may take an excessively long time. Consequently, conventional ATS systems employed in conjunction with such modern generators may be incapable of providing desired switching between such generators and other power sources in a satisfactory manner.
Therefore it would be advantageous if a new ATS system could be developed that allowed for proper switching between a modern generator and another power source such as a utility in a reasonable amount of time, despite the ability of the modern generator to operate at a frequency nearly identical to that of the utility. It would additionally be advantageous if such a new ATS system was not significantly more complicated in its design than conventional ATS systems and was not significantly more expensive to built or implement than conventional ATS systems.